The present invention relates to a heavy duty pneumatic tire, more particularly to a tread pattern comprising blocks provided with sipes and small holes capable of improving on-ice performance without sacrificing uneven wear resistance and durability.
In Japanese Patent Application Publication No. 2009-190677, a studless tire improved in the running performance on icy roads having low friction coefficients is disclosed. In this kind of a tire, blocks formed in the tread portion are provided with sipes. Owing to the sipes, the blocks can deform flexibly and scratch a road surface by their edges to improve driving force and braking force on the icy road.
Japanese Patent Application Publication Nos. 2009-190677 and 2006-168498 disclose passenger car tires, in which blocks in the tread portion are provided with small holes instead of sipes thereby to satisfy both of block rigidity and on-ice performance.
If the technique disclosed in Japanese Patent Application Publication No. 2006-168498 is applied to a heavy duty pneumatic tire used under high internal pressure and heavy loads, blocks suffer from uneven wear and tearing off in an early stage, therefore, it is difficult to provide sufficient durability.